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Planetary News: Extrasolar Planets (2009)COROT Spacecraft Finds Smallest Exoplanet YetFebruary 3, 2009
COROT, the European satellite tasked with detecting exoplanets, has found a planet less than twice the diameter of Earth orbiting a Sun-like star. It is the smallest terrestrial planet ever detected outside the Solar System, and the one most similar to our own. "This discovery is a very important step on the road to understanding the formation and evolution of our planet," said Malcolm Fridlund, ESA’s COROT Project Scientist. “For the first time, we have unambiguously detected a planet that is 'rocky' in the same sense as our own Earth. We now have to understand this object further to put it into context, and continue our search for smaller, more Earth-like objects with COROT," he added. The new planet, designate COROT-Exo-7b, is located very close to its parent star and completes each orbit in only 20 hours. As a result its surface temperature is scalding hot, possibly as high as 1500°C. Astronomers detected the new planet as it transited its parent star, dimming the light from the star as it passed in front of it. The composition of the planet is still under investigation. It may be rocky like Earth and covered in liquid lava, or it may be an "ocean world," a class of planets that are thought to be made up of water and rock in almost equal amounts. Given its surface temperature,, if the planet is indeed composed largely of water vapor it would be a very hot and humid place. The vast majority of the 300 odd planets found so far orbiting distant stars are gas giants similar to Jupiter, hundreds of times larger than Earth. Very few known exoplanets have a mass comparable to Earth’s and the solar system's other terrestrial planets – Venus, Mars, and Mercury. This is because terrestrial planets are relatively small and difficult to detect with methods that are sensitive to the planets' mass. Since most exoplanets were found with the mass-sensitive radial velocity method, it follows that most planets detected are massive. COROT, however, uses transit photometry, a method that measures a planet's size, not its mass, and is therefore better suited to detect smaller planets. In addition, COROT's location in space allows for long periods of uninterrupted observation, free from atmospheric interference. "Finding such a small planet was not a complete surprise”, said Daniel Rouan, researcher at the Observatoire de Paris Lesia, who coordinates the project with Alain Léger, from Institut d’Astrophysique Spatiale (Paris, France). “COROT-Exo-7b belongs to a class of objects whose existence had been predicted for some time. COROT was designed precisely in the hope of discovering some of these objects,” he added. COROT is a project of the French Space Agency CNES in partnership with ESA and several European nations. Did you like this story? Send
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